RU2746430C1 - Iron core of transformer - Google Patents

Abstract

FIELD: electrical engineering.

SUBSTANCE: invention relates to the field of electrical engineering. At least one of the plurality of transformer iron grain grain oriented electrical steel sheets stacked has: 1) a region in which trailing domains are formed in a direction intersecting the rolling direction and a region in which trailing domains are not formed; 2) the relative area R₀ from 0.10 to 3.0%, and the relative area R₀ is defined as the ratio of S₀ to S; 3) the relative area R_1a, which is 50% or more, and the relative area R_1a is defined as the ratio of S_1a to S₁, where S is the leaf area, S₁ is the area of ​​the region in which the closing domains are formed, S₀ is the area of ​​the region in which the closing domains are not formed. domains, and S_1a is the area of ​​the zone that is in the region of formation of the closing domains and in which the expansion value at the point of maximum deformation when magnetization is carried out in the rolling direction, with a maximum magnetic induction of 1.7 T and a frequency of 50 Hz, at least 2 × 10^-7 is greater than the expansion amount in the region in which no trailing domains are formed.

EFFECT: invention is aimed at suppressing the magnetostrictive vibration of the iron core due to mutual interference to reduce the noise level of the transformer.

3 cl, 10 tbl, 14 dwg

Description

The present invention relates to a transformer iron core made from stacked grain-oriented electrical steel sheets, and specifically relates to a transformer iron core whose magnetostrictive vibration can be reduced to suppress transformer noise.

State of the art

Traditionally, various methods have been studied to reduce the noise generated by transformers. In particular, iron cores are sources of noise even when unloaded. Accordingly, a number of technologies for making iron cores and grain-oriented electrical steel sheets used in iron cores have been developed to reduce the noise level.

The main cause of noise is the magnetostriction of grain oriented electrical steel sheets and the resulting vibration of the iron cores. Accordingly, various methods for suppressing vibration of iron cores have been proposed.

For example, JP 2013-087305 A (PTL 1) and JP 2012-177149 A (PTL 2) each propose a method for suppressing vibration of an iron core by sandwiching grain-oriented electrical steel sheets with a polymer or damping steel sheet.

JP H03-204911 A (PTL 3) and JP H04-116809 A (PTL 4) each propose a method for suppressing vibration of an iron core by stacking two types of steel sheets having different magnetostriction.

JP 2003-077747 A (PTL 5) proposes a method for suppressing vibration of an iron core by bonding stacked grain-oriented electrical steel sheets. JP H08-269562 A (PTL 6) proposes a method to reduce the magnetostriction amplitude by creating small internal stresses in the steel sheet.

List of cited documents

Patent Literature

PTL 1: JP 2013-087305 A

PTL 2: JP 2012-177149 A

PTL 3: JP H03-204911 A

PTL 4: JP H04-116809 A

PTL 5: JP 2003-077747 A

PTL 6: JP H08-269562 A

Disclosure of invention

Technical problem

The methods described in the documents PTL 1 to PTL 6 are believed to provide a certain effect of reducing magnetostriction or decreasing vibration of the iron core, but have several disadvantages.

By applying the method of sandwiching steel sheets with a polymer or a damping steel sheet, as suggested in PTL 1 and PTL 2, the size of the iron core is increased.

In the method that uses two types of steel sheets, as suggested in PTL 3 and PTL 4, it is necessary to strictly control the stacked steel sheets. This complicates the manufacturing process of the iron core and decreases productivity.

The process of bonding steel sheets together, as suggested in PTL 5, is time consuming. In addition, there is a possibility that an uneven load is applied to the steel sheets, which can deteriorate the magnetic properties.

With the method proposed in PTL 6, the magnetostriction amplitude can be reduced, but the magnetostrictive wave-like deformation is increased, resulting in an increase in noise caused by the magnetostrictive harmonic. Thus, the noise suppression effect is weak.

Thus, to reduce the vibration of the iron core and reduce the noise level of the transformer, it is advisable to use a mechanism other than traditional methods.

Solution to the problem

As a result of careful research, the present inventors discovered for the first time that by using two or more steel sheets with different magnetostrictive properties, it is possible to suppress the magnetostrictive vibration of the iron core due to mutual interference, and thus reduce the noise level of the transformer.

The present invention is based on the studies described above. The present invention provides:

1. An iron core of a transformer comprising a plurality of grain-oriented electrical steel sheets stacked, wherein at least one of the plurality of grain-oriented electrical steel sheets: (1) has a region in which trailing domains are formed in a direction crossing the rolling direction and a region, in which trailing domains are not formed; (2) has a relative area R ₀ defined as a ratio of S ₀ to S ranging from 0.10% to 3.0%, and (3) a relative area R _1a defined as a ratio of S _1a to S _{1 of} 50% or more, where S is the area of the grain-oriented electrical steel sheet, S ₁ is the area of the region in which the trailing domains are formed, S ₀ is the area of the region in which the trailing domains are not formed, and S _1a is the area of the zone that is in the region of the formation of the trailing domains. domains and in which the magnitude of expansion at the point of maximum deformation when magnetization is carried out in the rolling direction, with a maximum magnetic induction of 1.7 T and a frequency of 50 Hz, is at least 2x10 ^-7 greater than the magnitude of expansion in the region in which trailing domains.

2. The iron core of the transformer according to claim 1, wherein the angle of the closing domains with respect to the rolling direction is 60 ° to 90 °.

3. An iron core of a transformer according to claim 1 or 2, wherein the spacing between the closing domains in the rolling direction is 3 mm to 15 mm.

Beneficial effect

According to the present invention, the vibration of the iron core can be reduced and the noise level of the transformer can be reduced by using a mechanism different from conventional methods.

Brief Description of Drawings

In the attached drawings:

fig. 1 is a graph illustrating, by way of example, the expansion and contraction behavior of a grain-oriented electrical steel sheet magnetized with a maximum magnetic flux density of 1.7 T and a magnetization reversal frequency of 50 Hz;

fig. 2 is a schematic diagram of a grain-oriented electrical steel sheet as an iron core material used in Experiment 1;

fig. 3 is a graph of the dependence of the noise level (dB) of the transformer on the relative area R ₀ (%) of the area without closing domains (experiment 1);

fig. 4 is a graph of the dependence of the losses in the core (W / kg) of the transformer on the relative area R ₀ (%) of the area without closing domains (experiment 1);

fig. 5 is a schematic diagram of a grain-oriented electrical steel sheet as an iron core material used in Experiment 2;

fig. 6 is a schematic diagram of a grain-oriented electrical steel sheet used as a comparative in Experiment 2;

fig. 7 is a graph illustrating the expansion and contraction behavior when the grain-oriented electrical steel sheet is magnetized under conditions of a maximum magnetic flux density of 1.7 T and a frequency of 50 Hz (Experiment 2);

fig. 8 is a graph of the dependence of the noise level (dB) of the transformer on the difference in the expansion values (experiment 2);

fig. 9 is a schematic diagram of a grain-oriented electrical steel sheet as an iron core material used in Experiment 3;

fig. 10 is a graph of the dependence of the noise level (dB) of the transformer on the relative area R ₀ (%) of the area without closing domains in the range from 0% to 100% (experiment 3);

fig. 11 is a graph of the dependence of the noise level (dB) of the transformer on the relative area R ₀ (%) of the area without closing domains, for the range from 0% to 1% (experiment 3);

fig. 12 is a graph of the dependence of core losses (W / kg) of the transformer on the relative area R ₀ (%) of the area without closing domains, for the range from 0% to 100% (experiment 3);

fig. 13 is a graph of the dependence of losses in the transformer core (W / kg) on the relative area R ₀ (%) of the area without closing domains, for the range from 0% to 10% (experiment 3);

fig. 14 is a schematic diagram of embodiments of trailing domain formation regions in grain oriented electrical steel sheets according to the invention.

Detailed description of the invention

First of all, the magnetostriction of the grain-oriented electrical steel sheet will be described.

FIG. 1 is a graph illustrating, by way of example, the expansion and contraction behavior of the grain-oriented electrical steel sheet in the rolling direction when the grain-oriented electrical steel sheet is magnetized in the rolling direction, with a maximum magnetic flux density of 1.7 T and a frequency of 50 Hz.

Expansion and contraction of a steel sheet is usually caused by an increase or decrease in magnetic domains, called additional magnetic domains, which have components elongated in a direction perpendicular to the surface of the steel sheet and are spontaneously magnetized in the <100> <010> direction. Accordingly, one possible method for reducing the expansion and contraction of the steel sheet in the rolling direction is to suppress the formation of additional magnetic domains. The formation of additional magnetic domains can be suppressed by decreasing the deflection angle between the rolling direction and the [001] axis. However, there is a limit to how much the deflection angle can be reduced.

In this regard, the authors studied another method of suppressing the expansion and contraction of the entire iron core. In particular, regions differing in magnetostrictive properties are created in at least one of the grain-oriented electrical steel sheets constituting the iron core in order to suppress expansion and contraction of the entire iron core due to mutual interference between these regions. As a means of regulating the magnetostrictive properties, a method of forming closing domains in the direction intersecting the rolling direction was used. Since the trailing domains expand in the direction orthogonal to the rolling direction, the formation and disappearance of the trailing domains cause changes, that is, contraction and expansion of the steel sheet in the rolling direction.

The following describes experiments carried out to study the noise reduction of a transformer in this way.

Experiment 1

First, in a transformer iron core obtained by stacking grain-oriented electrical steel sheets subjected to magnetic domain grinding treatment, it was studied how the presence of a region in which no shorting domains are formed affects the noise level of the transformer.

FIG. 2 is a schematic diagram showing a grain-oriented electrical steel sheet 1 as an iron core material and an arrangement of trailing domains formed in the grain-oriented electrical steel sheet. A strip-like trailing domain forming region 10 extending from one end to the other end in the rolling direction of the grain-oriented electrical steel sheet 1 was formed at both end portions of the grain-oriented electrical steel sheet 1 in the width direction (orthogonal to the rolling direction). A region 20 (a region without trailing domains) in which trapping domains were not formed was formed in a portion other than the trailing domain forming region 10 created at the end portions of the grain-oriented electrical steel sheet 1 in the width direction and extending from one end to the other end of the sheet in the rolling direction of the grain-oriented electrical steel sheet 1.

A grain-oriented electrical steel sheet 1 as a transformer iron core material was manufactured according to the following procedure. First, a typical grain oriented electrical steel sheet having a thickness of 0.27 mm and not subjected to magnetic domain grinding was cut to a width of 100 mm in a direction orthogonal to the rolling direction, and then processed to beveled. When cutting the grain-oriented electrical steel sheet to obtain beveled edges, the surface of the steel sheet was irradiated with a laser at the upstream side of the cut line to create a trailing domain formation region 10. Linear laser scanning was performed in a direction orthogonal to the rolling direction as shown in FIG. 2. Laser irradiation was carried out at an interval (interval between irradiation lines) of 4 mm in the rolling direction. As a result of laser irradiation, a linear deformation 11 was created in each place irradiated with the laser.

Other conditions of laser exposure:

- laser: pulsed Q-switched laser;

- power: 3.5 mJ / pulse;

- interval between pulses (step interval): 0.24 mm.

Here, the pulse spacing denotes the distance between the centers of adjacent irradiation points.

To study the factors affecting the magnetostrictive properties, in the manufacture of grain-oriented electrical steel sheets, separate regions 20 were created without closing domains in the direction orthogonal to the rolling direction, having a width X varying in the range from 0 mm to 50 mm. When examining the closure domains by the Bitter method using a magnetic imaging device (MV-95, manufactured by Sigma Hi-Chemical, Inc.), it was found, as expected, that closure domains formed at the site where the deformation was generated. That is, linearly elongated trailing domains were formed in the region 10 of the trailing domain formation. The angle of the closing domains with respect to the rolling direction was 90 °, and the spacing between the closing domains in the rolling direction was 4 mm.

Then, the obtained grain-oriented electrical steel sheets 1 were stacked to form an iron core for a 1000 kVA rated transformer. The noise level and losses were estimated for each manufactured transformer, magnetized under the conditions: maximum induction 1.7 T and frequency of magnetization reversal 50 Hz.

FIG. 3 shows a graph of the dependence of the noise level (dB) of the transformer on the relative area R ₀ (%) of the region 20 without closing domains. Here, the relative area R _{0 of the} region 20 without trailing domains is defined as the ratio of the area S _{0 of the} region 20 without trailing domains to the area S of the grain-oriented electrical steel sheet 1 used. The area S of the grain-oriented electrical steel sheet 1 is the largest surface area (major surface) of the sheet in which the trailing domain formation region 10 and the trailing domain-free region 20 are provided (i.e., the surface area of the grain oriented electrical steel sheet 1 shown in FIG. 2).

From the results shown in FIG. 3, it can be concluded that in the presence of a region 20 without closing domains, even on a small area of the sheet surface, the noise level of the transformer is lower than the noise level in the absence of said region 20 without closing domains. The absence of the area 20 without trailing domains means that the region 10 forming the trapping domains occupies the entire surface of the grain-oriented electrical steel sheet. Conventional milling treatment of non-heat-resistant magnetic domains results in the formation of a trailing domain formation region 10 over the entire surface of the grain-oriented electrical steel sheet, that is, a region 20 without trailing domains is absent. The results shown in FIG. 3 indicate that with an excessively large relative area R _{0 of the} region 20 without closing domains, the noise level of the transformer is high.

FIG. 4 shows a graph of the dependence of the core loss (W / kg) of the transformer (iron loss) on the relative area R ₀ (%) of the region 20 without closing domains. The region without trailing domains is created by reducing the area in which trapping domains are formed, that is, the region that has been processed to refine the magnetic domains. Therefore, when the relative area R _{0 of} the non-terminating domain increases, the core loss of the transformer increases as shown in FIG. 4. However, from the results shown in FIG. 4, it is clear that with a small relative area R _{0, the} losses in the transformer core increase very insignificantly.

These results show that the noise level can be reduced without significantly increasing iron loss by forming two regions with different magnetostrictive properties, i.e., a region of closing domains and a region without closing domains, in a grain-oriented electrical steel sheet and limiting the relative area R ₀ areas without trailing domains with a specific range.

The reason why the noise of the transformer was reduced by creating a region without shorted domains is explained below. In the region in which the closure domains are formed, the formation and disappearance of the closure domains and the disappearance and formation of additional magnetic domains cause the expansion and contraction of the steel sheet. Since the closing domains disappear as a result of magnetization, the steel sheet expands in the rolling direction when magnetized in the region where the closing domains are formed. Meanwhile, in the region in which the closing domains are not formed, the expansion and contraction of the steel sheet is controlled upon disappearance and formation of additional magnetic domains. Since additional magnetic domains are formed as a result of magnetization, the steel sheet is compressed in the rolling direction when magnetized in a region without closure domains. Thus, the region of formation of the closing domains and the region without the closing domains demonstrate the opposite character of expansion and contraction. Therefore, by creating both the closing domain forming region and the non-closing domains in one steel sheet, compression of the entire steel sheet is suppressed, and thus the noise level is reduced.

The reason for the insignificant increase in the core loss of the transformer when the relative area R _{0 of the} region without shorting domains is small is disclosed below. In a single sheet magnetic property test (single sheet test) to evaluate the magnetic property of a grain oriented electrical steel sheet, the steel sheet was magnetized in the rolling direction with a sine wave, and the steel loss was measured. Accordingly, if even in a small area there is a region without closing domains, that is, a region not subjected to the refinement of magnetic domains, the losses in iron are noticeably reduced. On the other hand, in a real transformer, there are other factors that lead to an increase in iron loss, in addition to the presence of a region without closure domains, such as undulating deformation during magnetization and deviation of the magnetization direction from the rolling direction. Thus, in a transformer, the influence of the region without closing domains on the iron loss is relatively small. For this reason, the effect of introducing a region without trailing domains was not as significant as when testing a single sheet.

Experiment 2

Then the influence of the shape of the magnetostrictive curve in the region of formation of the closing domains on the noise level of the transformer was studied. As a result of studying various parameters, it was found that the noise level of the transformer can be effectively reduced by limiting the compression value to a certain range at the extremum point of the magnetostrictive curve at 1.7 T and 50 Hz. This experiment will be described below.

FIG. 5 is a schematic diagram showing a grain-oriented electrical steel sheet 1 as an iron core material and an arrangement of trailing domains formed in the grain-oriented electrical steel sheet. A trailing domain forming region 10 extending from one end to the other end of the grain-oriented electrical steel sheet 1 in the rolling direction was formed at both end portions of the grain-oriented electrical steel sheet 1 in the width direction (direction orthogonal to the rolling direction). A region other than the trailing domain formation region 10 is a region 20 (a region without trailing domains) in which trapping domains are not formed. The width of the region 20 without trailing domains in the direction orthogonal to the rolling direction was 15 mm.

A grain-oriented electrical steel sheet 1 as a transformer iron core material was manufactured according to the following procedure. First, a typical grain-oriented electrical steel sheet having a thickness of 0.23 mm and not subjected to a magnetic domain comminution treatment was cut to a width of 150 mm, then processed to beveled. When bevelling the edges of the grain-oriented electrical steel sheet, the surface of the steel sheet was irradiated with a laser from the cut line to create a trailing domain formation region 10. Linear laser scanning was performed in the direction orthogonal to the rolling direction as shown in FIG. 5. Laser irradiation was carried out at an interval (interval between irradiation lines) of 5 mm in the rolling direction. As a result of laser irradiation, linear deformation 11 was created in each laser-irradiated area 11. When the laser power was varied in the range from 100 W to 250 W, a plurality of grain-oriented electrical steel sheets were obtained, differing from each other in the amount of compression in the region of forming the closing domains.

Other conditions of laser exposure:

- laser: single mode fiber laser;

- deflection speed: 5 m / s;

- power: from 100 W to 250 W (see table 1).

Linearly elongated trailing domains were formed in the region 10 of the trailing domain formation. The angle of the closing domains with respect to the rolling direction was 90 °, and the spacing between the closing domains in the rolling direction was 5 mm.

For comparison, a grain-oriented electrical steel sheet having no region without trailing domains was obtained by forming trailing domains in the entire steel sheet, as shown in FIG. 6.

To determine the magnetostrictive properties of each of the sections, namely, the section for forming the closing domains and the section without the closing domains, a grain-oriented electrical steel sheet was prepared, the entire surface of which was irradiated with a laser, under the same conditions as the above-mentioned grain-oriented electrical steel sheet, and was also prepared a grain-oriented electrical steel sheet that has not been irradiated with a laser. Using a laser Doppler vibrometer, the amount of expansion and contraction of each obtained grain-oriented electrical steel sheet was measured when magnetized under conditions of a frequency of 50 Hz and a maximum magnetic induction of 1.7 T. As representative examples, the results of measuring the expansion amount for respective grain-oriented electrical steel sheets obtained under three different laser irradiation conditions and a grain-oriented electrical steel sheet not irradiated with a laser are shown in FIG. 7 and are presented in table 1.

Table 1

No. Power
(W) Expansion at the point of maximum deformation
(10 ^-7 ) Expansion difference
(10 ^-7 ) Scope without trailing domains Formation area
trailing domains one 100 -five -four one 2 180 -five 2 7 3 250 -five 3 eight

Particular attention was paid to the amount of expansion at the point of maximum deformation (point of maximum deformation), according to the nature of the measured expansion and contraction, (hereinafter referred to simply as “the amount of expansion”), which for each sample is given in Table 1. “Difference of expansion values” (Δλ = λ ₁ - λ ₀ ), which is defined as the difference between the expansion (λ ₁ ) in the region of formation of the closing domains and the expansion (λ ₀ ) in the region without closing domains, is also given in Table 1. The expansion value with a minus sign indicates the amount of contraction.

The results shown in FIG. 7 and Table 1 show that in the region of formation of the closing domains, the expansion amount at the point of maximum deformation increases with increasing laser power, that is, an increase in the amount of introduced deformation is observed.

Next, the obtained grain-oriented electrical steel sheets 1 were stacked to form an iron core for a 1200 kVA rated transformer. The noise level of each manufactured transformer, magnetized at a maximum magnetic induction of 1.7 T and a frequency of 50 Hz, was evaluated.

FIG. 8 is a graph showing the dependence of the noise level of the transformer on the difference in the values of expansion (Δλ) at the point of maximum deformation. The results in FIG. 8 shows that if Δλ is 2x10 ^-7 or more, the noise level of the transformer is effectively reduced. The point in FIG. 8 in which the difference in the expansion amounts is 0 corresponds to the measured value for the one shown in FIG. 6 grain oriented electrical steel sheet having no area without trailing domains.

Experiment 3

Then the influence of the relative area R _{0 of the} region without closing domains on the noise level of the transformer was studied.

FIG. 9 is a schematic diagram showing a grain-oriented electrical steel sheet 1 as an iron core material and an arrangement of trailing domains formed in the grain-oriented electrical steel sheet 1. In the grain-oriented electrical steel sheet 1, two closure domains 10 were formed to extend from one end to the other end of the grain-oriented electrical steel sheet 1 in the rolling direction. The regions other than the trailing domain formation regions 10 were regions 20 (regions without trailing domains) in which no trailing domains were formed. The width of one of the two regions without trailing domains in the direction orthogonal to the rolling direction was X, and the width of the other region without trailing domains in the direction orthogonal to the rolling direction was 2X. By varying the X value, grain oriented electrical steel sheets were obtained differing in the relative area R _{0 of the} region without trailing domains (i.e., two regions without trailing domains) in the range from 0% to 100%. If the relative area R ₀ is 0%, this means that only the region of formation of the trailing domains is present, and the region without trailing domains is absent. If the relative area R ₀ is 100%, this means that only a region without trailing domains is present, and a region for forming trailing domains is absent.

A grain-oriented electrical steel sheet 1 as a transformer iron core material was manufactured according to the following procedure. First, a typical grain oriented electrical steel sheet having a thickness of 0.30 mm and not subjected to magnetic domain grinding was cut to a width of 200 mm in a direction orthogonal to the rolling direction, and then processed to beveled. When cutting the grain-oriented electrical steel sheet to obtain beveled edges, the surface of the steel sheet was irradiated with an electron beam from the upstream side of the cut line to create a closure domain formation region 10. Linear scanning was performed with an electron beam in a direction orthogonal to the rolling direction as shown in FIG. 9. Electron beam irradiation was performed at an interval (interval between the irradiation lines) of 4 mm in the rolling direction. As a result of irradiation with a laser beam, a linear deformation 11 was created in each area irradiated with an electron beam.

Based on the results of the preliminary study, the beam current was set to 2 mA or 15 mA. As shown in the results of experiment 2, if the difference in the expansion values is 2x10 ^-7 or more, the noise level of the transformer is effectively reduced. To obtain the required difference in the expansion values, the minimum beam current must be 2 mA. With an increase in the beam current, the difference in the expansion values additionally increases. However, if irradiation is performed at an excessive amount of beam current, the deformation of the steel sheet increases, and as a result, the steel sheet may become unsuitable as an iron core material. The upper limit of the beam current at which the shape of the steel sheet as the iron core material can be maintained is 15 mA. Therefore, the difference in the amount of expansion in the obtained grain-oriented electrical steel sheet is 2x10 ⁻⁷ or more, regardless of which of the beam current values is used.

Other conditions for electron beam irradiation:

- accelerating voltage: 60 kV;

- scanning speed: 10 m / s.

Linearly elongated trailing domains were formed in the region 10 of the trailing domain formation. The angle of the closing domains with respect to the rolling direction was 90 °, and the spacing between the closing domains in the rolling direction was 4 mm.

The obtained grain oriented electrical steel sheets 1 were stacked to form an iron core for a 2000 kVA rated transformer. The noise level and core loss of each manufactured transformer, magnetized at a maximum magnetic induction of 1.7 T and a frequency of 50 Hz, were evaluated.

FIG. 10 shows a graph of the dependence of the noise level (dB) of the transformer on the relative area R ₀ (%) of the area without closing domains. FIG. 11 shows a graph of the dependence of the noise level (dB) of the transformer on the relative area R ₀ (%) of the area without closing domains in the range from 0% to 1%. That is, in FIG. 11 is an enlarged view of a portion of the graph of FIG. 10. According to the results in FIG. 10 and 11, if the relative area R ₀ is 0.10% or more, the noise level of the transformer can be effectively reduced regardless of the amount of beam current, that is, the amount of deformation introduced.

FIG. 12 shows a graph of the dependence of the core loss (W / kg) of the transformer on the relative area R ₀ (%) of the area without closing domains. FIG. 13 shows a graph of the dependence of the core loss (W / kg) of the transformer on the relative area R ₀ (%) of the area without closing domains in the range from 0% to 10%. That is, FIG. 13 is an enlarged view of a portion of the graph of FIG. 12. According to the results in FIG. 12 and 13, if the relative area R ₀ is 3.0% or less, the increase in core loss of the transformer can be suppressed regardless of the amount of beam current, that is, regardless of the amount of deformation introduced.

According to the presented results, if the relative area R _{0 of the} area without closing domains is 0.10% or more and 3.0% or less, the noise level of the transformer can be reduced while suppressing the increase in core loss of the transformer regardless of the amount of deformation introduced.

The technologies used in the present invention are described in detail below. The following description is intended to illustrate preferred embodiments of the present invention, which should not be construed as limiting.

Iron core transformer

A transformer iron core according to one disclosed embodiment is a transformer iron core comprising a plurality of grain-oriented electrical steel sheets stacked, at least one of the grain-oriented electrical steel sheets satisfying the conditions described below. The design and other characteristics of the iron core of the transformer are not limited, that is, the core can be of any design and other characteristics.

Textured Electrical Steel Sheet

At least one of the grain-oriented electrical steel sheets as an iron core material for a transformer must have a closing domain formation region and a non-closing domain region that satisfy the conditions described below. The area of formation of the closing domains and the area without the closing domains of the steel sheet differ in magnetostrictive properties, as mentioned above. If one of the grain-oriented electrical steel sheets used in the iron core has portions different from each other in magnetostrictive properties, expansion and contraction of the iron core can be suppressed, and the noise level of the transformer can be reduced. In this case, the rest of the grain-oriented electrical steel sheets in the iron core can be any.

The grain-oriented electrical steel sheet used as the iron core material is processed to the required size. Even in the case where the grain-oriented electrical steel sheet (original sheet) has a closing domain forming region and a non-closing domains region before processing, the grain-oriented electrical steel sheet may end up having only one of the regions, namely, a closing domain forming region or a non-closing domain. domains depending on which part of the original sheet is cut the grain-oriented electrical steel sheet as the iron core material. Thus, a grain oriented electrical steel sheet as an iron core material must be manufactured in accordance with the conditions described below.

The thickness of the grain-oriented electrical steel sheet included in the iron core according to the present invention is not limited, and the sheet may have any thickness. Even when the thickness of the steel sheet is changed, the number of disappearing closing domains and the number of additional magnetic domains formed are unchanged. Thus, the effect of reducing the noise level can be achieved regardless of the thickness of the sheet. However, from the viewpoint of reducing the core loss, it is desirable that the grain-oriented electrical steel sheet be thin. Therefore, the thickness of the grain oriented electrical steel sheet is preferably 0.35 mm or less. In the meantime, if the grain-oriented electrical steel sheet has at least a predetermined thickness, it is easier to handle and improve the workability in the manufacture of the iron core. Thus, a grain-oriented electrical steel sheet thickness of 0.15 mm or more is preferable.

Trailing domain

The closing domains are formed in a direction intersecting the rolling direction of the grain-oriented electrical steel sheet. In other words, the trailing domains extend in a direction intersecting the rolling direction. Trailing domains are usually linear. The angle (tilt angle) of the closing domains with respect to the rolling direction is not limited, however, it is preferably 60 ° to 90 °. Here, the angle of the closing domains with respect to the rolling direction denotes the angle between the linearly elongated closing domains and the rolling direction of the grain-oriented electrical steel sheet.

The closing domains are preferably spaced in the rolling direction of the grain-oriented electrical steel sheet. The spacing (linear spacing) between the trailing domains in the rolling direction is not limited, however, it is preferably 3 mm to 15 mm. Here, the spacing between the trailing domains denotes the distance between one trapping domain and an adjacent trapping domain. The spacing between the trailing domains can vary, however, the spacing is preferably equal.

One grain oriented electrical steel sheet may include one or more closure domains. If there are multiple trailing domain forming regions in one grain-oriented electrical steel sheet, the angle of inclination and the spacing between the trailing domains in each trailing domain forming region may be the same or different. If several grain-oriented electrical steel sheets are used in the iron core and each has a closing domain forming region, the angle and spacing between the closing domains in the closing domain forming region in each grain-oriented electrical steel sheet may be the same or different.

In the present invention, the term “region in which trailing domains are formed” means a region in which a plurality of trailing domains are present extending in the direction intersecting the rolling direction and spaced apart in the rolling direction. For example, if the trailing domains are formed sequentially at an interval from one end to the other end of the grain-oriented electrical steel sheet 1 in the rolling direction of the grain-oriented electrical steel sheet 1, as shown in FIG. 2, the term “region in which trailing domains are formed” is used to refer to a strip-like region (hatched portion) in which a group of trailing domains are formed. In the description of the present invention, the term "area of formation of trailing domains" is used interchangeably with the term "area in which trapping domains are formed".

At least one of the grain-oriented electrical steel sheets constituting the iron core of the transformer according to the present invention must have a closing domain and a non-closing domain, as well as a relative area R ₀ and a relative area R _1a , which must satisfy the conditions described below.

Relative area R ₀ : 0.10% to 3.0%

The relative area R ₀ , defined as the ratio of S ₀ to S, should be from 0.10% to 3.0%, where S is the area of the _{grain-oriented electrical steel sheet and S 0 is the} area of the region in which the trailing domains are not formed. If the relative area R _{0 is} less than 0.10%, the effect of reducing the noise level due to the interaction between the region without trailing domains and the region of forming the trailing domains is insufficient. If the relative area R _{0 is} more than 3.0%, the fraction of the area of formation of the closure domains decreases, so that the grinding effect of the magnetic domains is insufficient and the core loss increases.

Relative area R _1a : 50% or more

The relative area R _1a , defined as the ratio of S _1a to S ₁ , must be 50% or more, where S ₁ is the area of the region in which the trailing domains are formed, and S _1a is the area of the zone of the region in which the trailing domains are formed and in which the expansion amount is at least 2x10 ^-7 greater than the expansion amount in the region in which no trailing domains are formed. In other words, the relative area R _{1a of the} part of the region of formation of the closing domains, in which the "difference in expansion values" (Δλ = λ ₁ - λ ₀ ), defined as the difference between the value of expansion (λ ₁ ) in the region of formation of the closing domains and the value of expansion (λ ₀ ) in the region without trailing domains, is 2x10 ^-7 or more, should be 50% or more of the entire region of formation of trailing domains. Here, the expansion amount denotes the expansion amount at the point of maximum deformation during magnetization in the rolling direction, with a maximum magnetic flux density of 1.7 T and a frequency of 50 Hz.

As mentioned previously, when the grain-oriented electrical steel sheet is magnetized, the additional magnetic domains expand in the direction of the sheet thickness, thereby causing the grain-oriented electrical steel sheet to contract in the rolling direction. In addition, the closing domains present in the steel sheet expand in the direction orthogonal to the rolling direction, whereby the steel sheet contracts in the rolling direction due to the presence of the closing domains. Accordingly, when the trailing domains disappear due to magnetization, the steel sheet expands in the rolling direction. This expansion of the sheet counteracts the contraction caused by the formation of additional magnetic domains, accordingly, the compression of the grain-oriented electrical steel sheet in the rolling direction can be effectively reduced, and hence the noise of the transformer can be suppressed.

To achieve the specified noise suppression effect, the relative area R _1a must be 50% or more. To further enhance this effect, the relative area R _1a is preferably 75% or more. There is no upper limit for the relative area of R _1a , and the relative area of R _1a may be 100%.

Expansion difference: 2x10 ^-7 or more

The relative area R _1a is defined as the relative area of the zone in which the difference in the magnitude of the expansion is 2x10 ^-7 or more. If the difference in the expansion amounts is less than 2x10 ^-7 , the above vibration suppression effect is low, and the noise level of the transformer cannot be sufficiently reduced. The upper limit of the difference in compression values is not set However, if the difference is excessively large, the absolute value of magnetostriction in at least one of the regions will be large, which can cause an increase in noise. In addition, under conditions in which there is a large difference in the amount of compression, the steel sheet may deform and become unusable as an iron core material. Thus, the difference in the amount of compression is preferably 5x10 ^-6 or less.

At least one of the grain oriented electrical steel sheets constituting the iron core of the transformer must satisfy the above conditions. If the proportion of grain-oriented electrical steel sheets satisfying the above conditions of the total number of grain-oriented electrical steel sheets is high, the expansion and contraction of the entire iron core can be further reduced, and a higher noise reduction effect can be achieved. Therefore, the proportion is preferably 50% or more, and more preferably 75% or more. There is no upper limit for the specified proportion, and the proportion may be 100%. Here, the proportion is defined as the ratio of the weight of the grain oriented electrical steel sheets satisfying the conditions of the present invention to the total weight of all the grain oriented electrical steel sheets constituting the iron core of the transformer.

The reason why the magnetostriction change in the present invention is determined on the basis of the expansion amount "when magnetized with a maximum magnetic flux density of 1.7 T and a frequency of 50 Hz" is that grain-oriented electrical steel transformers are usually used with a magnetic induction of 1.7 T. ... At lower magnetic induction, noise is less problematic. In addition, under the aforementioned magnetization conditions, the features of magnetostriction due to the crystal orientation and structure of the magnetic domains of the electrical steel sheet are noticeably manifested. Therefore, the amount of expansion under these conditions is an effective indicator of magnetostrictive properties.

Although the number of disappearing closing domains and the number of formed additional magnetic domains change in absolute value depending on the magnetic induction during magnetization and the frequency of magnetization reversal, their relative proportion is unchanged. That is, if the number of disappearing closing domains is small, the number of additional magnetic domains formed is also small. Thus, the effect of suppressing expansion and contraction can be achieved regardless of the density of the magnetizing magnetic flux. Therefore, the conditions for using the iron core for the transformer according to the present invention are not limited to 1.7 T and 50 Hz, and can be anything.

When the closure domains are formed, the core loss is reduced due to the chopping effect of the magnetic domains. Accordingly, if the formed shorting domains satisfy the conditions of the present invention, the shorting domains will help reduce core loss. Thus, the present invention is also not limited in terms of reducing the core loss.

Method of forming trailing domains

The method for forming the trailing domains is not limited and can be anything. An example of a method for forming the closing domains is the introduction of deformation in the regions in which the closing domains are to be formed. Examples of methods for introducing deformation include shot blasting, water blasting, laser processing, electron beam processing, and plasma processing. By introducing linear deformation in the direction intersecting the rolling direction, closing domains can be formed in the direction intersecting the rolling direction.

The method for creating the region without closing domains is not limited, and the region without closing domains may be a portion of the steel sheet not subjected to deformation. Even if the entire surface of the steel sheet is machined to introduce deformation, by adjusting the machining mode, it is possible to avoid deforming a certain portion of the steel sheet to create an area without trailing domains. For example, by introducing deformation with a laser or an electron beam, it is possible to prevent deformation of a certain portion of the sheet by deflecting the focus away from the surface of the steel sheet. As another example, the introduction of deformation in a certain area of the sheet can be prevented by reducing the pressure during shot blasting or water blasting.

The moment of time of the formation of the closing domains is not limited and can be any. For example, the trailing domains can be formed before or after cutting the grain-oriented electrical steel sheet. In the case of the formation of closing domains, before cutting, it is necessary to select a narrow roll and adjust the cutting position so that the relative area R ₀ and the relative area R _1a satisfy the above conditions. From a performance point of view, it is preferable to form the trailing domains after cutting the sheet.

Magnetostrictive properties can also be altered by changing crystal orientation or film tension to control the state of additional magnetic domain formation. However, partial control by crystal orientation or film tension is very difficult and not commercially feasible. The present invention provides a very simple method for forming closure domains in a grain-oriented electrical steel sheet, which can effectively improve the production capacity of the iron cores of transformers.

The region of forming the trailing domains need not extend from one end to the other end of the sheet in the rolling direction as shown in FIG. 2. The shape of the area of formation of the closing domains is not limited to rectangular and can be any.

The location of the closing domain formation region in the plane of the grain-oriented electrical steel sheet is not limited and may be anything. For more effective suppression of expansion and contraction, it is preferable to position the trailing domain formation region and the trailing domain-free region in a direction orthogonal to the rolling direction. In other words, it is preferable that the boundary between the trailing domain formation region and the region without trailing domains adjacent to the trailing domain formation region has a component in the rolling direction.

Examples of

Three types of grain-oriented electrical steel sheets with a width of 160 mm and a thickness of 0.23 mm, 0.27 mm and 0.30 mm were prepared, and each of these grain-oriented electrical steel sheets was irradiated with an electron beam to form closure domains. The arrangement of the areas of formation of the trailing domains was selected from six options (a) - (f) shown in FIG. 14. According to embodiment (a), one grain-oriented electrical steel sheet has one region for forming the trailing domains. In embodiments (b) and (c), there are two trailing domain forming regions in one grain-oriented electrical steel sheet. In embodiments (e) and (f), there are three trailing domain forming regions in one grain-oriented electrical steel sheet. According to embodiment (d), in one grain-oriented electrical steel sheet, there are four trailing domain forming regions. In each embodiment, the region (s) other than the region (s) of forming the trailing domains is a region without trailing domains.

Tables 2 to 4 show the relative area R ₀ , defined as the ratio of the area S _{0 of the} area in which the closing domains are not formed to the area S of the grain-oriented electrical steel sheet, and the beam current for creating each area of formation of the closing domains, according to the variants of the arrangement of the forming areas trailing domains. Here, the relative area of the closing domain formation region is defined as the ratio (%) of the area of the closing domain formation region to the area of the grain-oriented electrical steel sheet. In samples 11-14, the relative area R _{1a was} varied by changing the areas of region 1 and region 2, while the other conditions were the same.

Other conditions for electron beam irradiation:

- accelerating voltage: 60 kV;

- scanning speed: 32 m / s;

- spacing between irradiation lines: 5 mm.

The number (volume) of closure domains introduced can be adjusted by changing conditions such as accelerating voltage, beam current, scan rate, and formation interval. In one example, the number of closure domains introduced was adjusted by varying the beam current. Since the compression pattern of the steel sheet depends on the number of inserted closing domains, the effect on the compression pattern does not change as long as the volume of the inserted closing domains remains unchanged, regardless of the control parameter. Several samples (Nos. 1, 10 and 21) were comparative and were not exposed to electron beam irradiation.

Then, the magnetostrictive properties in each region were evaluated and the "difference in the expansion values" (Δλ = λ ₁ - λ ₀ ) was calculated, that is, the difference between the expansion (λ ₁ ) in the region of formation of the closing domains and the expansion (λ ₀ ) in the region without closing domains. domains. The magnetostrictive properties in each region were evaluated on samples 100 mm wide and 500 mm long cut from a grain-oriented electrical steel sheet and irradiated with an electron beam under the same irradiation conditions. Test specimens were prepared from identical grain oriented electrical steel sheets. Using a laser Doppler vibrometer, magnetostriction (expansion and contraction of a steel sheet) was measured when the sample was magnetized from a demagnetized state (0 T) with an alternating current at a maximum magnetic induction of 1.7 T and a frequency of 50 Hz. The calculated difference in the expansion values is given in tables 2 - 4.

Tables 2 to 4 show the relative area R _1a determined as the ratio of S _1a to S ₁ in the obtained grain-oriented electrical steel sheet. Here S ₁ is the area of the region in which the closing domains are formed, and S _1a is the area of the zone of the region in which the closing domains are formed, namely, the area of the zone in which the magnitude of expansion at the point of maximum deformation when magnetization is carried out in the direction of rolling with maximum with a magnetic induction of 1.7 T and a frequency of 50 Hz, at least 2x10 ^-7 more than the expansion value at the point of maximum deformation in the region in which closing domains are not formed when magnetization is carried out in the rolling direction with a maximum magnetic induction of 1.7 T and a frequency of 50 Hz.

The obtained grain-oriented electrical steel sheet was then used to make a transformer iron core. Beveled grain oriented electrical steel sheets cut from a roll 160 mm wide were stacked to form a "tripod" iron core of a three-phase transformer. The overall dimensions of the iron core were as follows: width 890 mm, height 800 mm, and stack thickness 244 mm.

The proportion (%) of grain oriented electrical steel sheets obtained according to the above procedure, with respect to the total iron core, is shown in Tables 2 to 4. An iron core in which the specified proportion was 100% was made by stacking only grain oriented electrical steel sheets irradiated with electron beam according to the above procedure. The iron core, in which the specified proportion was less than 100%, was made by stacking not only one or more grain-oriented electrical steel sheets irradiated with an electron beam, according to any of the options shown in Figs. 14, but also one or more grain oriented electrical steel sheets irradiated over the entire surface with an electron beam with a beam current of 7 mA.

Then, an excitation coil was wound around the obtained iron core, the iron core was magnetized under the conditions shown in Tables 5 to 10, the noise level of the transformer and the transformer core loss (no-load loss) were measured under different magnetization conditions. Magnetization was carried out with alternating current with a frequency of 50 Hz or 60 Hz with three different maximum inductions, namely, 1.3 T, 1.5 T and 1.7 T.

The noise level was measured at six locations, namely, in front and behind each of the three legs of the iron core. The measuring point was at a height of 400 mm and at a distance of 300 mm from the surface of the iron core. The average noise level measured at six locations is shown in Tables 5 to 7. The results of core loss measurements are shown in Tables 8 to 10.

From the results shown in Tables 5 to 10, it can be concluded that in each iron core of the transformer satisfying the conditions of the present invention, the noise level was lower and the core loss was lower than in the comparative examples.

Table 5

No. Noise level (dB) transformer Note 50 Hz 60 Hz 1.3 T 1.5 T 1.7 T 1.3 T 1.5 T 1.7 T one 50.0 55.0 60.0 53.0 59.0 65.0 Comparative example 2 50.0 55.0 60.0 53.0 59.0 65.0 Comparative example 3 45.0 50.0 55.0 48.0 54.0 60.0 Example four 47.0 52.0 57.0 50.0 56.0 62.0 Example five 44.0 49.0 54.0 47.0 53.0 59.0 Example 6 45.0 50.0 55.0 48.0 54.0 60.0 Example 7 50.0 55.0 60.0 53.0 59.0 65.0 Comparative example eight 50.0 55.0 60.0 53.0 59.0 65.0 Comparative example nine 44.5 49.5 54.5 47.5 53.5 59.5 Example

Table 6

No. Noise level (dB) transformer Note 50 Hz 60 Hz 1.3 T 1.5 T 1.7 T 1.3 T 1.5 T 1.7 T 10 50.0 55.0 60.0 53.0 59.0 65.0 Comparative example eleven 45.5 50.5 55.5 48.5 54.5 60.5 Example 12 46.5 51.5 56.5 49.5 55.5 61.5 Example 13 47.5 52.5 57.5 50.5 56.5 62.5 Example fourteen 49.5 54.5 59.5 52.5 58.5 64.5 Comparative example fifteen 48.0 53.0 58.0 51.0 57.0 63.0 Example sixteen 45.0 50.0 55.0 48.0 54.0 60.0 Example 17 48.5 53.5 58.5 51.5 57.5 63.5 Example eighteen 44.0 49.0 54.0 47.0 53.0 59.0 Comparative example nineteen 44.0 49.0 54.0 47.0 53.0 59.0 Example twenty 44.0 49.0 54.0 47.0 53.0 59.0 Comparative example

Table 7

No. Noise level (dB) transformer Note 50 Hz 60 Hz 1.3 T 1.5 T 1.7 T 1.3 T 1.5 T 1.7 T 21 50.0 55.0 60.0 53.0 59.0 65.0 Comparative example 22 50.0 55.0 60.0 53.0 59.0 65.0 Comparative example 23 46.5 51.5 56.5 49.5 55.5 61.5 Example 24 45.5 50.5 55.5 48.5 54.5 60.5 Example 25 45.5 50.5 55.5 48.5 54.5 60.5 Example 26 49.5 54.5 59.5 52.5 58.5 64.5 Comparative example 27 44.0 49.0 54.0 47.0 53.0 59.0 Example 28 45.5 50.5 55.5 48.5 54.5 60.5 Example 29 45.5 50.5 55.5 48.5 54.5 60.5 Example thirty 44.5 49.5 54.5 47.5 53.5 59.5 Comparative example 31 46.5 51.5 56.5 49.5 55.5 61.5 Comparative example

Table 8

No. Core loss (W / kg) transformer Note 50 Hz 60 Hz 1.3 T 1.5 T 1.7 T 1.3 T 1.5 T 1.7 T one 0.610 0.810 1,040 0.790 1,030 1,330 Comparative example 2 0.530 0.730 0.960 0.710 0.950 1,250 Comparative example 3 0.490 0.690 0.920 0.670 0.910 1,210 Example four 0.490 0.690 0.920 0.670 0.910 1,210 Example five 0.493 0.693 0.923 0.673 0.913 1.213 Example 6 0.493 0.693 0.923 0.673 0.913 1.213 Example 7 0.491 0.691 0.921 0.671 0.911 1.211 Comparative example eight 0.490 0.690 0.920 0.670 0.910 1,210 Comparative example nine 0.500 0.700 0.930 0.680 0.920 1,220 Example

Table 9

No. Core loss (W / kg) transformer Note 50 Hz 60 Hz 1.3 T 1.5 T 1.7 T 1.3 T 1.5 T 1.7 T 10 0.700 0.920 1,170 0.900 1,170 1,510 Comparative example eleven 0.580 0.800 1,050 0.780 1,050 1,390 Example 12 0.580 0.800 1,050 0.780 1,050 1,390 Example 13 0.580 0.800 1,050 0.780 1,050 1,390 Example fourteen 0.581 0.801 1.051 0.781 1.051 1,391 Comparative example fifteen 0.580 0.800 1,050 0.780 1,050 1,390 Example sixteen 0.581 0.801 1.051 0.781 1.051 1,391 Example 17 0.581 0.801 1.051 0.781 1.051 1,391 Example eighteen 0.640 0.860 1,110 0.840 1,110 1,450 Comparative example nineteen 0.583 0.803 1.053 0.783 1.053 1,393 Example twenty 0.640 0.860 1,110 0.840 1,110 1,450 Comparative example

Table 10

No. Core loss (W / kg) transformer Note 50 Hz 60 Hz 1.3 T 1.5 T 1.7 T 1.3 T 1.5 T 1.7 T 21 0.710 0.990 1,300 0.940 1,280 1,710 Comparative example 22 0.600 0.880 1.190 0.830 1,170 1,600 Comparative example 23 0.600 0.880 1.190 0.830 1,170 1,600 Example 24 0.600 0.880 1.190 0.830 1,170 1,600 Example 25 0.600 0.880 1.190 0.830 1,170 1,600 Example 26 0.600 0.880 1.190 0.830 1,170 1,600 Comparative example 27 0.602 0.882 1.192 0.832 1.172 1.602 Example 28 0.602 0.882 1.192 0.832 1.172 1.602 Example 29 0.607 0.887 1.197 0.837 1.177 1.607 Example thirty 0.620 0.900 1,210 0.850 1.190 1,620 Comparative example 31 0.620 0.900 1,210 0.850 1.190 1,620 Comparative example

List of reference positions

1 - grain oriented electrical steel sheet

10 - area of formation of closing domains

11 - linear deformation

20 - area without trailing domains.

Claims (9)

1. An iron core for a transformer containing a plurality of grain-oriented electrical steel sheets stacked wherein at least one of the plurality of grain oriented electrical steel sheets has: (1) a region in which trailing domains are formed in a direction intersecting the rolling direction and a region in which trailing domains are not formed; (2) the relative area R ₀ , defined as the ratio of S ₀ to S, ranging from 0.10 to 3.0%; and (3) the relative area R _1a , defined as the ratio of S _1a to S _1, equal to 50% or more, where S is the area of the grain-oriented electrical steel sheet, S ₁ is the area of the region in which the trailing domains are formed, S ₀ is the area of the region in which trailing domains are not formed, and S _1a is the area of the zone that is in the region of formation of the trailing domains and in which the amount of expansion at the point of maximum deformation during magnetization in the rolling direction, with a maximum magnetic induction of 1.7 T and a frequency of 50 Hz, is at least 2x10 ^-7 greater than the amount of expansion in the region in which closing domains are not formed. 2. An iron core for a transformer according to claim 1, wherein the angle of the closing domains with respect to the rolling direction is 60 ° to 90 °. 3. An iron core for a transformer according to claim 1 or 2, wherein the spacing between the closing domains in the rolling direction is 3 to 15 mm.

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